The most frequently occurring brain malignancies in adults are metastatic brain cancers (e.g., from primary melanoma, lung cancer, breast cancer, gastrointestinal cancer (e.g., pancreatic or colorectal), kidney cancer, bladder cancer, certain sarcomas, or testicular or germ cell tumors) followed by glioblastoma (GBM). GBM is the most aggressive primary brain cancer, which generally has a poor prognosis with median survival of about 14 months, despite aggressive treatment (Filippini et al. Neuro Oncol. 2008; 10(1):79-87). Currently diagnosis of brain tumors is made with brain biopsy if possible and the analysis of cerebrospinal fluid (CSF) for the presence of cancer cells (cytology). CSF can be accessed readily for longitudinal disease monitoring during and after therapy. However, the currently used method of CSF analysis has moderate sensitivity, is non-quantitative and technically challenging. There is presently no routine way to subtype the malignancy and monitor molecular changes from CSF indicating the need for more accurate and reliable biomarkers and methods.